Three weeks ago I got my !! BAN ME NOW FOR SWEARING !! together and invested into a cheap cadence, hrm and speed computer.

Now, everything has been gravy- except my heart rate readings. At my maximum effort (cement legs and lungs on fire) my heart rate rarely goes past 165 bpm. Theoretically, according to my height, weight and age, my anaerobic (100% hr max) should be 180-200 bpm. Over the three weeks I have used the computer, my max heart rate readings in interval sprint training has actually dropped from 170 to 165.

What's wrong with me?

My background is pretty average; student; active training schedule; proper nutrition; 23 male, 183 cm, 79 kg. My average heart rate during endurance rides is high 130s and my resting hr is recorded at 65 bpm. I may happen to partake in a few social spliffs during the day with housemates, which I believe could be the culprit but I can't find any science to prove it.

Well, my HRmax goes up by one every year, not down, so there goes the theory!

HR is a very individual thing. Mine rarely goes over 173 when on a commute, but on the mtb it redlines (like today) at 182 and I can sustain within a couple of BPM either side of 170 for half an hour in a race when fit. Yet my late cousin in his early 70s could sustain 180 for 25km climbing and hit 200bpm in the sprints in his local C grade.

I'd say don't sweat it. It takes a good 3 years to get properly adapted to cycling, not sure how long you've been at it, but I'd just treat the info you're getting as being in the information gathering phase. I had no idea what I could really do until I recorded my first race on my Garmin and downloaded it later - and completely blew away my (limited) expectations about what was a sustainable heart rate for me!

Your slow heart rate for your age quite possibly is a side effect, but is the *least* of your concerns.

Mental illness is a major risk from cannabis use, let alone the high tar content's impact on cardiovascular health. The vast majority of those in Manly Hospital's East Wing have cannabis use in their history. You only have one brain, and how well it functions determines much of how your life goes ... whether it goes well or sucks. Don't screw with it.

Well, it's not a competition to see who has a higher heart rate.If you are performing well and your heart rate is low that is a good thing. In my experience, a low heart rate means you are just not trying, and could push a lot harder.When you do push hard enough, for long enough, you'll begin to understand why the expression "world of pain" is such a central part of cycling lore.